In an OLED display device, each of pixel units generally comprises three subpixels. Each subpixel comprises an OLED that is driven by a driving module to emit a corresponding color of light. The OLED display device allows each pixel unit to display different luminance and colors by controlling parameters such as brightness and color saturation of the light emitted from the OLED in each subpixel.
Generally, the driving module comprises a plurality of transistors and at least one capacitor. FIG. 1 illustrates a driving module that comprises a small number of transistors and a capacitor. As shown in FIG. 1, the driving module comprises a switching transistor T1, a driving transistor M1 and a storage capacitor C1. In the driving module shown in FIG. 1, a current for driving the OLED to emit light is expressed as:
      I    =                  β        2            ⁢                        (                      Vgs            -            Vth                    )                2              ,
where Vgs indicates a voltage difference between a gate and a source of the driving transistor M1, β indicates a parameter in connection with a process parameter and a feature size of the driving transistor M1, and Vth indicates a threshold voltage of the driving transistor M1.
Generally, in the existing OLED display device, the OLEDs in the subpixels are driven by individual driving modules and emit light simultaneously. Such a configuration causes the number of the driving modules to be equal to that of the subpixels in each pixel unit, so that the number of the driving modules is relatively large, resulting in that large numbers of transistors, storage capacitors and signal lines are required to be provided in each pixel unit and a large area is occupied by each pixel unit, which counts against improvement of the pixel density of the OLED display device.